This invention relates generally to the field of oil production. More specifically, this invention relates to a method for improving recovery of oil, preferably heavy oil, by accelerating gravity drainage using vibrational energy generated from a well fracture.
Steam-Assisted Gravity Drainage (SAGD) is one of the thermal methods of recovering heavy oil or bitumen with steam, where the oil contacted by steam drains down to a horizontal producing well by gravity. In the SAGD process of recovering bitumen, two horizontal wells are drilled in parallel close to each other, near the bottom of the bitumen pay zone, preferably one above the other. (Butler, R. M., Thermal Recovery of Oil and Bitumen, GravDrain Inc., Calgary, Canada (1997)). As shown in FIG. 1, steam is injected through the upper horizontal well 6, to heat the bitumen, lowering its viscosity, and create a steam chamber 1. As the steam chamber 1 grows, the lower viscosity oil 3 generated at its ceiling 5 and side walls 7 drains downward by gravity 9, and is produced through the lower horizontal well 8. Since the steam injector and the oil producer are very close to each other, any forced injection or production of fluids to speed up oil production will cause a rapid coning, or production of steam instead. Therefore, oil production has to be left to gravity as the sole driving force. While the oil recovery efficiency for SAGD is known to be fairly good, its major drawback is the slowness of oil production, because it relies solely on gravity to produce oil.
In the vapor extraction process (VAPEX), a solvent is used instead of steam to reduce the bitumen viscosity, but the oil production relies on gravity force alone and is slow. (Butler, R. M., and Mokrys, I. J., xe2x80x9cA new process (VAPEX) for recovering heavy oils using hot water and hydrocarbon vaporxe2x80x9d, J. Canadian Petrol. Tech., 30 (1), 97-106 (1991)). A newer related process, steam and gas push (SAGP), uses steam plus a noncondensible gas and again relies on gravity drainage. (Butler, R. M., xe2x80x9cThe Steam and Gas Push (SAGP),xe2x80x9d Paper 97-137 presented at the 48th Annual Technical Meeting of the Petroleum Society of CIM, Calgary, Jun. 8-11, 1997).
Seismic vibration in the range of 5-120 Hz is known to sometimes improve oil recovery from mature oil reservoirs. Laboratory coreflood and imbibition test results have shown oil recovery improvement due to vibration. Typically, a large mechanical vibrator pounds the ground surface to transmit seismic energy to the reservoir zone. However, due to the typically long distance between the surface and the pay zone, only a very small fraction of the vibrational energy reaches the pay zone. Furthermore, a large fraction of the vibration generated is wasted as a surface (Rayleigh) wave, which may also have environmentally detrimental effects.
To transmit vibrational energy more effectively, a vibration source is sometimes lowered downhole to the pay zone to generate vibration at the wellbore. Even then, only a small fraction of reservoir volume receives a significant amount of vibrational energy. This is because vibration generated from the downhole vibrator, which is essentially a point source, propagates spherically in all directions and diminishes very quickly due to spherical divergence.
In U.S. Pat. No. 2,670,801 (Sherborne) sonic waves are generated in a well to vibrate an oil-bearing formation to increase recovery, and in U.S. Pat. No. 3,002,454 (Chesnut) explosives are detonated in a horizontal well to increase vertical permeability by generating fractures. U.S. Pat. No. 5,297,631 (Gipson) discloses a method for oil formation stimulation by sudden release of high pressure gas from a gun in a well. Further, U.S. Pat. No. 5,396,955 (Howlett) discloses a method wherein permeability of a reservoir is enhanced by acoustic waves targeted at the reservoir. Accordingly, there is a need for a low-cost method of accelerating oil production in gravity drainage processes and thereby reducing the steam or solvent requirement, as well as the project duration, for better process economics.
This invention provides a method of improving oil recovery comprising the steps of (a) creating at least one fracture in the vicinity of at least one well in a hydrocarbon pay zone; (b) installing a vibration source device in at least one well; (c) generating a fluid oscillation in the fracture using the vibration source device whereby the fluid oscillation in the fracture generates vibrational energy that increases gravity drainage in the hydrocarbon pay zone; and (d) removing oil from the hydrocarbon pay zone. Preferably, this method is used with steam-assisted gravity drainage or vapor extraction gravity drainage processes, but may be applied to single-well processes, such as huff-n-puff or cyclic steam stimulation processes.